Detection of word-line leakage in memory arrays
Techniques and corresponding circuitry are presented for the detection of wordline leakage in a memory array. In an exemplary embodiment, a capacitive voltage divider is used to translate the high voltage drop to low voltage drop that can be compared with a reference voltage to determine the voltage drop due to leakage. An on-chip self calibration method can help assure the accuracy of this technique for detecting leakage limit.
1. A memory device, including:
a memory array having memory cells formed along a plurality of word-lines;
a voltage generation circuit to provide a first voltage level to an output node;
decoding circuitry, whereby the first voltage level from the output node can be selectively applied to the word-lines; and
a word-line defect detection circuit, including:
a capacitive voltage divider, connected between the output node and a low voltage level;
a first switch, through which an intermediate node of the capacitive voltage divider is connected to receive a voltage derived from the first voltage level; and
a comparator having a first input connected to the intermediate node of the capacitive voltage divider and a second input connected to receive a reference voltage,
wherein the memory device performs a process for the detection of defective word-lines, the including: a pre-charge phase, where the decoding circuitry connects the output node to apply the voltage level to a pattern of a first set of the word-lines and the first switch is closed; a subsequent isolation phase, where the output node is left to float and the first switch is open; and a subsequent detection phase, where the first switch is open and the output of the comparator indicates the value of the voltage level on the intermediate node relative to the reference voltage.
2. The memory device of claim 1 , wherein the voltage generation circuit includes:
a charge pump circuit that generates the first voltage level; and
regulation circuitry, including a first voltage divider circuit connected on one side to the output node and on the other side connectable to the low voltage level, wherein the first switch connects the intermediate node of the capacitive voltage divider to an intermediate node of the first voltage divider circuit.
3. The memory device of claim 2 , the regulation circuit further including a second switch whereby the first voltage divider circuit is connectable to the low voltage level, wherein the second switch is closed during the pre-charge phase and open during the isolation and detection phases.
4. The memory device of claim 1 , wherein the cells of the memory array are formed of a plurality of erase blocks and the first set of word-lines correspond to a first erase block.
5. The memory device of claim 1 , wherein the voltage pattern is the application of a high-voltage on alternate word-lines of the first erase block and the low voltage level on the other word-lines of the first erase block.
6. The memory device of claim 4 , wherein the voltage pattern is the application of a high-voltage on all of word-lines of the first erase block while the substrate of the first erase block is held at the low voltage level.
7. The memory device of claim 1 , further comprising:
a state machine, wherein the word-line defect detection circuit is implemented as part of the state machine.